It should already be attached to the LCD, if not then you can purchase the adhesive and attach it to the LCD yourself

Step 4 "We highlighted buttons with pink circles for easy recognition." except that there's no pink circles. ummm?

If you're talking about the touch keys at the bottom, slide a thin tool between the glass and the touch keys on the underside of the glass carefully as it's held by adhesive

Great suggestion!

Your friend is lying to you and doesn't know anything he is saying either, you probably should believe everything people say.

While this suggestion is more professional, it requires more time and resources that aren't completely necessary, or maybe not for your average repairer. Of all the S4 screens I've replaced I use the basic adhesive that comes with the glass from my supplier and that has enough strength to hold the glass in place when it is applied correctly. This was interesting though, thanks!

That's unfortunate, sometimes in some unlucky cases the LCD or digitiser tries to come up with the glass which probably means it needs to be heated up for longer with the heatgun.

You'll need to leave holes otherwise you may cover the sensors or other components to the phone.